Considering you're planning to switch distro's, I'd focus on backing up "generic" system-wide configs like ssh, samba, apache, etc (provided you actually modified them)
I'd probably leave the user configs - ~/.* alone since it might vary among different distro's. Not sure.
I wouldn't use dd... since it's a block device copy and would be designed to make a perfect copy of your current setup. Not something very useful when you want to switch distro's ("restoring" would bring back your system as it is right now)
So... I'd copy all personal files of course.
Commands like rsync, scp are great for backing up files over a network. If you just want to grab your personal files and put them into a file you can tar them up with a command like this:
tar -zcf backupfile.tar.gz ~/Music ~/Documents ~/Movies ~/Etc
-z == gzip compression; -c == create archive; -f == archive filename
Dating the tar file is a wise idea.